Question

Two rifles are fired from the same
place at a difference of 11 min.
45 seconds. But a man who is
coming towards the same place
in a train hears the second sound
after 11 minutes. Find the speed
of the train (Assuming speed of
sound = 330 m/s).
(1) 72 km/h (2) 36 km/h
3) 81 km/h
(4) 108 km/h

Answer 1

answer is option :3

Distance travelled by man-train in 11 minute = distance traveled by sound in (11 min 45 sec - 11 min) = 45 sec.

Let the speed of train be x kmph.

Now,

Or, x*11/60 = (45/3600)*330*18/5;

Or, x = 81 kmph.